1. Field of the Invention:
This invention relates in general to electromagnetic transducers, and more specifically to a taut armature resonant electromagnetic transducer.
2. Description of the Prior Art:
Portable communication devices, such as pagers, have generally used cylindrical motors which spin an eccentric counterweight or "pancake" motors which utilize eccentric armature weighting to generate a tactile, or "vibratory" alert. Such an alert is desirable to generate a "silent" alert which is used to alert the user that a message has been received without disrupting persons located nearby. While such devices have worked satisfactorily for many years and are still widely being used, several issues limit a much broader use. Motors, when used to provide a tactile, "silent", alert are hardly "silent", but rather provide a perceptible acoustic output due in part to the high rotational frequency required for the operation of the motor to spin the counterweight sufficiently to provide a perceptible tactile stimulation. Likewise, such motors, as a result of their inherent design, have generally consumed a substantial amount of energy for operation. This has meant that the motor must be switched directly from the battery for operation, and significantly impacts the battery life that can be expected during normal operation of the portable communication devices.
Recently, a new generation of non-rotational, radial electromagnetic transducers was described by Mooney et al., U.S. Pat. No. 5,107,540, and McKee et al., U.S. Pat. No. 5,327,120, which significantly reduced the energy consumed from a battery for operation as a tactile alerting device. In addition, since the electromagnetic transducer operated at a sub-audible frequency which maximized the tactile sensation developed when the transducer is coupled to a person, a truly silent non-disruptive alert was provided. Because the size and shape of the radial electromagnetic transducer was similar to that of a pancake motor, retrofits of the new device could readily be more accommodated in established communication devices with little change to the driving circuitry or mechanics.
While the new generation of non-rotational, radial electromagnetic transducers have significantly reduced the energy consumption, and have also significantly reduced the sound developed when in actual operation, there is yet a need for an electromagnetic transducer which provides an even lower energy consumption, while maintaining the performance characteristics of the radial electromagnetic transducers.